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Date: Sun, 07 Nov 2010 23:41:37 +0100 From: Andreas Schwab <schwab@...ux-m68k.org> To: Andi Kleen <andi@...stfloor.org> Cc: Jim <jim876@...all.nl>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, gcc@....gnu.org Subject: Re: gcc 4.5.1 / as 2.20.51.0.11 miscompiling drivers/char/i8k.c ? Andi Kleen <andi@...stfloor.org> writes: > Jim <jim876@...all.nl> writes: > >> After upgrading my Dell laptop, both OS+kernel the i8k interface was giving >> nonsensical output. As it turned out it's not the kernel but compiler >> upgrade which broke this. >> >> Guys at Archlinux have found the underlying cause (but don't seem to have >> submitted a patch yet): >> https://bbs.archlinux.org/viewtopic.php?pid=780692#p780692 >> gcc seems to optimize the assembly statements away. >> >> And indeed, applying this patch makes the i8k interface work again, >> i.e. replacing the asm(..) construct by asm volatile(..) > > The compiler really should not optimize the asm away, because > it has both input and output arguments which are later used. > "asm volatile" normally just means "don't move significantly" The asm fails to mention that it modifies *regs. Andreas. -- Andreas Schwab, schwab@...ux-m68k.org GPG Key fingerprint = 58CA 54C7 6D53 942B 1756 01D3 44D5 214B 8276 4ED5 "And now for something completely different." -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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